AD8138
OPERATIONAL DESCRIPTION
DEFINITION OF TERMS
C
F
R
F
R
G
+IN
–OUT
Common-mode voltage refers to the average of two node
voltages. The output common-mode voltage is defined as
V
OUT, cm
= (V
+OUT
+
V
−OUT
)/2
Balance is a measure of how well differential signals are
matched in amplitude and exactly 180° apart in phase. Balance
is most easily determined by placing a well-matched resistor
divider between the differential voltage nodes and comparing
the magnitude of the signal at the divider’s midpoint with the
magnitude of the differential signal (see Figure 41). By this
definition, output balance is the magnitude of the output
common-mode voltage divided by the magnitude of the output
differential mode voltage:
+D
IN
V
OCM
–D
IN
AD8138
R
G
–IN
R
F
C
F
+OUT
R
L, dm
V
OUT, dm
Figure 42. Circuit Definitions
Differential voltage refers to the difference between two node
voltages. For example, the output differential voltage (or
equivalently output differential-mode voltage) is defined as
V
OUT, dm
= (V
+OUT
−
V
−OUT
)
where
V
+OUT
and
V
−OUT
refer to the voltages at the +OUT and
−OUT terminals with respect to a common reference.
01073-041
Output Balance Error
=
V
OUT
,
cm
V
OUT
,
dm
Rev. F | Page 16 of 24
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